main.cpp

00001 // use WDT to measure drift of RTC and IRC
00002 // seems WDT ISR will only fire once
00003 #include "mbed.h"
00004 
00005 DigitalOut led1(LED1);
00006 uint32_t ticks;
00007 
00008 void kick() {
00009     __disable_irq();
00010     LPC_WDT->WDFEED = 0xAA;
00011     LPC_WDT->WDFEED = 0x55;
00012     __enable_irq();
00013 }
00014 
00015 void isr_wdt(void) {
00016     ticks++;
00017     led1 = 1;
00018     LPC_WDT->WDMOD |= (1<<3);
00019  //    LPC_WDT->WDMOD &= ~(1<<2);
00020  //   kick();
00021 }
00022 
00023 void wdt_init() {
00024     LPC_WDT->WDCLKSEL = 0x2;               // Set CLK src 0 IRC  1 PCLK   2 RTC
00025    // uint32_t clk = SystemCoreClock / 16;    // WD has a fixed /4 prescaler, PCLK default is /4
00026     LPC_WDT->WDTC = 0xfffffff;    // max countdown
00027     LPC_WDT->WDMOD = 0x01;  // enable but no reset
00028     NVIC_SetVector(WDT_IRQn, (uint32_t)&isr_wdt);
00029     NVIC_ClearPendingIRQ(WDT_IRQn);
00030     NVIC_EnableIRQ(WDT_IRQn);
00031     kick();
00032 }
00033 
00034 int main() {
00035     uint32_t t,t0=0,us,us0,prev;
00036     int ppm;
00037     Timer tmr;
00038     tmr.start();
00039     printf("hello %x\n",LPC_WDT->WDMOD);
00040     wait(1.0);
00041     wdt_init();
00042     prev=LPC_WDT->WDTV;
00043     while(1) {
00044         t=LPC_WDT->WDTV;
00045         us = tmr.read_us();
00046         if (t0==0 || t0 == 255) {
00047             t0 = t;
00048             us0 = us;
00049         }
00050         double tf = (t0-t)/8192.;  //  /8192 for rtc   1000000 for IRC
00051         double secs = 1.e-6*(us-us0);
00052         ppm = 1.e6*(tf-secs)/secs;
00053         printf("ticks %d %d %u %d us  %x %d ppm \n",ticks,prev-t,t0-t,us-us0,t,ppm);
00054         prev=t;
00055         wait(2.0);
00056     }
00057 }